The invention relates to a gas valve unit for adjusting a volumetric gas flow supplied to a gas burner of a gas appliance, in particular a gas cooking appliance, wherein the gas valve unit has a gas inlet, at least two open/close valves, at least two throttle points and a gas outlet.
Gas valve units of the aforesaid type are described, for example, in the publications EP0818655A2 and WO2004063629A1. By means of gas valve units of this type the volumetric gas flow supplied to a gas burner of a gas appliance can be controlled in a plurality of stages. In this case the volumetric gas flow possesses a reproducible magnitude at each stage. The effective through-flow cross-section of the gas valve unit overall—and hence the magnitude of the volumetric gas flow—is adjusted by opening or closing specific open/close valves of the gas valve unit and thereby releasing or interrupting the gas flow through specific throttle openings.
In the known gas valve units according to EP0818655A2 and WO2004063629A1, a plurality of parallel secondary gas lines branch off after the gas inlet, each of said lines having an open/close valve and a throttle point. All of the secondary gas lines lead into a common gas outlet. In another embodiment variant of EP0818655A2, a plurality of throttle points are connected in series and each is provided with a bypass. In addition, an open/close valve is arranged in each bypass. The known embodiment variants serve to adjust the through-flow cross-section of the overall gas valve unit in a plurality of stages, whereby the open/close valves are opened and closed individually and independently of one another. In this arrangement switching operations are provided in which one open/close valve must be opened and another open/close valve closed at exactly the same time. During practical operation switching operations of said kind result in the volumetric gas flow being briefly reduced or increased to an undesired value and consequently the flame at the gas burner is temporarily reduced or increased in size.